When the Ledson Fire ignited Monday east of Santa Rosa, it ran straight into terrain the 2017 Nuns Fire and 2020 Glass Fire had already devastated — and the dense dead timber those disasters left behind complicated the effort to contain this week's blaze, Cal Fire officials said.

The 16.5-acre Ledson Fire in Sonoma County and the 78.6-acre Hardin Fire in Napa County's Pope Valley were both nearly contained by Wednesday morning — but the Ledson Fire's path through overlapping burn scars on the western slope of the Mayacamas Mountains offered an early-season signal about how Northern California's accumulated fire history reshapes the next fight before it even begins.

The Ledson Fire ignited shortly after 1 p.m. Monday near North Pythian Road in the Kenwood area east of Santa Rosa, according to the Press Democrat. Firefighters stopped its forward progress that afternoon; by Wednesday morning it was 80 percent contained and held at 16.5 acres, Cal Fire spokesperson Jason Clay said. About 45 firefighters — four engines, two hand crews and two water tenders — remained on scene Wednesday.

"Significant progress has been made," Clay told the Press Democrat. "Crews will remain on scene until the fire is fully contained and all remaining hot spots are secured."

The vegetation the Ledson Fire consumed sat within the overlapping footprints of the Nuns Fire, which tore through the Mayacamas Mountains in October 2017, and the Glass Fire, which burned the same ridgelines in September 2020. The back-to-back fires left heavy concentrations of dead and downed trees across the terrain — material that created additional hazards for ground crews even as the fire itself stayed relatively small, the Press Democrat reported.

Twenty-five miles northeast in Napa County, the Hardin Fire broke out Monday afternoon near Pope Canyon Road in Pope Valley. It was 95 percent contained Wednesday morning at 78.6 acres, according to Cal Fire — more than four times the size of the Ledson Fire, despite aircraft dropping retardant and ground crews responding. The Hardin Fire spread initially through dry grass at a moderate rate before crews could establish containment lines, the SF Chronicle reported. No evacuation orders were issued for the Hardin Fire.

The Ledson Fire moved quickly enough to prompt Sonoma County Sheriff's Office to issue an evacuation order Monday afternoon for Zone SON-3H3, where structures near Highway 12 and North Pythian Road were threatened. That order was downgraded to a warning and lifted Monday evening after crews halted the fire's spread. No structures were damaged and no injuries were reported in either fire, according to Cal Fire.

The causes of both fires remain under investigation.

The fires broke out one day before a National Weather Service heat advisory that took effect Tuesday across the North Bay's interior mountains and valleys, with widespread highs forecast in the 90s and some locations expected to reach the low 100s, the SF Chronicle reported. The advisory was scheduled to remain in effect through 10 p.m. Tuesday.